1. Field of the Invention
The present invention relates to an adaptor circuit for power supply.
2. Description of Related Art
A typical microprocessor-cored computer system, such as a personal computer or a workstation computer, is turned on and off by a switch device that mechanically connects/disconnects a power supply of the computer system to/from an external power source, such as AC 110V. The power supply is connected to the external power source and transforms the external voltage into a predetermined DC level, such as +3.3V, ±5V and ±12V, and the computer system is turned on to perform various programs and functions.
As known by persons skilled with computers, mainly, power supplies are either an Advanced Technology Extended (ATX) power supply or a Balanced Technology Extended (BTX) power supply. A motherboard of a computer can be coupled to an ATX power supply via a 20-pin ATX power connector and two 4-pin ATX power connectors. The ATX power supply provides +3.3V, +/−5V, +/−12V, +5V_SB (stand by), PS_ON (power supply on) signal, and PWR_GOOD (power good) signal. When the ATX power supply is turned on, the PS_ON signal is at a low level, and the PWR_GOOD signal is at a high level but there is a delay of 100-500 ms for the other voltages. When the ATX power supply is turned off or put on standby, the PS_ON signal is at a low level, and +3.3V, +/−5V, +/−12V are turned off.
The PWR_GOOD signal is a 5V TTL (transistor-transistor logic) voltage signal for driving chipsets on a motherboard. But some of the chipsets of the motherboard need a 3.3V driving voltage, therefore the PWR_GOOD signal cannot drive these chipsets.
What is needed is an adaptor circuit for power supply which can provide both 5V and 3.3V power good signals to drive chipsets on the motherboard.